1. Field of the Invention
This invention generally relates to autocollimating alignment telescopes and, more particularly, to structural and functional improvements in such telescopes.
2. Description of the Prior Art
An autocollimating alignment telescope integrates an autocollimator and an alignment telescope in a single optical measuring instrument. As is well known, a telescope enables a viewer, looking through an eyepiece which is focused at a focal plane, to see a far-away object whose light is focused at the same focal plane by a stationary objective lens. An alignment telescope includes a reticle located at the focal plane, and a focusing lens which is movable relative to the stationary objective lens. The position of the focusing lens influences the focal length of the objective lens, and focuses the image of the far-away object on the reticle. In a typical application where a plurality of far-away objects are sequentially viewed through the alignment telescope and their respective images focused on the reticle, the objects may be aligned along an optical axis of the alignment telescope, or be arranged in any desired orientation.
With the addition of an autocollimator, light-reflecting surfaces, such as mirrors, on exterior objects can be aligned perpendicularly to the optical axis of the alignment telescope. A collimator simulates a far-away object by generating parallel light rays. More specifically, a light source is located at the focal plane of a stationary objective lens, and diverging light emitted by the light source is converted to parallel light rays by the objective lens. An autocollimator transmits such parallel light rays for reflection onto the exterior mirror, and receives the reflected rays. More specifically, the light source directs the diverging light through a reticle and through the stationary objective lens where it is converted to parallel light rays. The parallel light rays impinge on the exterior mirror which reflects the rays back through the objective lens and focuses the reflected rays onto another reticle which is located at the focal plane of an eyepiece. Thus, a viewer, looking through the eyepiece, can check the angular position in space of the exterior mirror and, hence, of the object on which the mirror is mounted.
Since both the individual autocollimator and the individual alignment telescope utilize some of the same optical components, e.g. a stationary objective lens, an eyepiece, at least one reticle, such components need not be duplicated in an integrated autocollimating alignment telescope, and can be separately used either in the alignment telescope mode of operation, or in the autocollimating mode of operation. The light source, of course, is not needed in the alignment telescope mode. In the autocollimating mode, the movable focusing lens must be held in a fixed position. A beam splitter is typically employed in the autocollimating alignment telescope to provide two optical paths along which the various light rays travel.
Although the known autocollimating alignment telescopes were generally satisfactory for their intended purposes, they have not proven to be altogether convenient to use. For example, the light source, as noted above, has to be energized in the autocollimating mode, but not in the alignment telescope mode. Typically, the light source was energized by electrical power supplied from an electrical outlet and into which an electrical plug was inserted. The plug was mounted at one end of a cable whose other end was either directly connected to the light source, or was connected to the latter through an electrical switch. To energize the light source, the user either had to manually insert the plug into the outlet, or manually flip the switch. To deenergize the light source, the user either had to manually remove the plug from the outlet, or manually flip the switch again. In a typical optical measuring situation where one was required to change often from the alignment telescope mode to the autocollimating mode, and vice versa, it was extremely burdensome to require the user to repeatedly perform the above-described extra manual motions when changing modes.
Furthermore, the known autocollimating alignment telescopes were essentially custom-made instruments and not readily adaptable to different applications. For example, a user would typically advise the instrument manufacturer which of the aforementioned reticles were to be used in the instrument, and the instrument would then be supplied with the reticles permanently and precisely epoxied in place. The user had little recourse if he or she desired to use different reticles, because of their permanent installation. Thus, an instrument might be provided with a dark field reticle, but if a bright field reticle were instead desired, there was no way, short of returning the instrument to the manufacturer for a reworking, that this could be achieved. Similarly, there were reticles with center dots, with concentric circles, or with cross-lines, etc., and once the known instruments were manufactured with one of these types of reticles, the user was compelled to use this reticle type no matter what the particular application.
The known autocollimating alignment telescopes also caused user discomfort in that a user was compelled always to view an object through an eyepiece whose position on the instrument was fixed. The instrument has an elongated barrel extending along a major axis, and the eyepiece was either centered on the major axis so that the user could view the object by positioning his or her eye on the major axis, or the eyepiece was located above, and at a right angle to, the major axis so that the user could view the object by positioning his or her eye above the major axis. The fixed position of the eyepiece meant that the user had to use the instrument by always positioning his or her eye either colinearly or perpendicularly to the major axis. There are optical measurement situations where the user would like the option as to how to position his or her eye, or would like to change the position of his or her eye, but the known instruments do not permit this versatility.
The known autocollimating alignment telescopes also were prone to jamming of, and damage to, the focusing lens when the same was moved inside and along the barrel and struck mechanical stops which defined end-limiting positions for the focusing lens. The focusing lens was moved by a gear drive coupled to a manually-turnable focusing knob. When the focusing lens abutted against either stop in either one of its end-limiting positions, the possibility existed that damage to the focusing lens, or stripping of the gears, or jamming of the focusing lens against the stop could occur, particularly if the user forcefully turned the knob and forced the focusing lens against the stop with a high impact force. Also, the known autocollimating alignment telescopes typically used a gear drive with a single gear ratio, e.g. a predetermined high number of turns of the focusing knob was required to move the focusing lens from one to the other of its end-limiting positions. This was highly undesirable and time consuming.